Materials with excellent stretchability and elasticity are needed to manufacture a variety of durable articles such as, for example, sport apparel and furniture upholstery. Stretchability and elasticity are performance attributes that function to effectuate a closely conforming fit to the body of the wearer or to the frame of the item. Maintenance of the conforming fit during repeated use, extensions and retractions at body temperatures is very desirable.
A material is typically characterized as elastic where it has a high percent elastic recovery (that is, a low percent permanent set) after application of a biasing force. Ideally, elastic materials are characterized by a combination of three important properties: a low percent permanent set, a low stress or load at strain, and a low percent stress or load relaxation. That is, elastic materials are characterized as having the following properties (1) a low stress or load requirement to stretch the material, (2) no or low relaxing of the stress or unloading once the material is stretched, and (3) complete or high recovery to original dimensions after the stretching, biasing or straining is discontinued.
Spandex is a segmented polyurethane elastic material known to exhibit nearly ideal elastic properties. However, not only is spandex cost prohibitive for many applications, it also exhibits poor resistance to moisture at elevated temperature. This, in turn, compromises the ability to dye fabrics made from it using conventional aqueous dying processes. For example, the thermosol dying process is an aqueous process that employs temperatures in excess of 200 C. Fabrics made from spandex cannot withstand the conditions of this process without a diminution in their elastic properties and as such, fabrics made from spandex must be processed at a lower temperature. This results in higher process costs and less uptake of dye into the fabric.
Elastic materials comprising polyolefins, e.g., polyethylene, polypropylene, polybutylene, etc., are known. These include, among others, U.S. Pat. Nos. 4,425,393, 4,957,790, 5,272,236, 5,278,272, 5,324,576, 5,380,810, 5,472,775, 5,525,257, 5,858,885, 6,140,442 and 6,225,243 all of which are incorporated herein by reference. These disclosures notwithstanding, however, a present need exists for cost-effective elastic articles having good resistance to moisture at elevated temperatures.